A Possible Metabolic Basis for the Control of Body Weight

IT has been suggested that both weight and metabolism are regulated, in part, by a common mechanism: substrate or "futile" cycling. The sensitivity of many regulatory mechanisms in metabolic pathways can be improved by the existence of a substrate cycle in which the activity of a key enzyme in a metabolic pathway is opposed by a reverse reaction catalyzed by a different enzyme. However, since cycling involves an obligatory loss of chemical energy as heat, this loss may also be quantitatively important in "burning off" excess energy. It is thought that rates of cycling are increased before exercise, after exercise, . . .